The reaction of H.sub.2 with C0 to produce methane, which is promoted by a Raney nickel catalyst, is conventionally carried out in a tube reactor which generally consists essentially of a stainless steel tube through which the gases are passed in contact with the catalyst. The reaction is highly exothermic, there being a 50.degree. C temperature rise per 1% increase C0 in the synthesis gas. Sintering or recrystallization of the catalyst can occur as a result of the high temperatures, leading to decreased activity. One of the problems encountered in developing a commercial process is how to increase the output of methane without overheating or poisoning the catalyst.
Usually, in the prior art methods, the catalyst is in the shape of pellets from which the heat has to be removed by gaseous conduction. Another method proposed is to coat the interior of 304 stainless steel reaction tubes with Raney nickel by flame spraying. A thin coat of Raney nickel, about 0.5 mm thick, is deposited by this method, and then activated by leaching with 2% Na0H solution. Excessive temperature buildup in the catalyst is prevented by removing the heat of reaction through the tubes to a heat exchange fluid. While successful, the method for preparing the tube in this manner has a number of drawbacks. The method of flame spraying is slow, about one foot of tube is coated per hour; the process is labor intensive and hence expensive; and causes dimentional distortions in the substrate tube. A relatively thin layer of Raney nickel is deposited so that the reactivation of the catalyst by abraiding the depleted surface and regenerating is limited.